In the design and manufacture of a deodorant or antiperspirant stick product, it is preferable that the top of the stick have a convex contour and that its cross-sectional shape be circular or oval. The convex shape is desired so that the product is comfortable to apply upon its first application and has a good appearance to the consumer. The oval cross-section makes application more efficient by requiring a minimum number of strokes to apply the product evenly. Furthermore, with such products it is preferred by consumers to have a package that dispenses the product using an elevator/screw system, commonly referred to as a swivel-up package. Such a package is typically equipped with an elevator platform, disposed within the package at its bottom end, having a spindle in threaded engagement therewith. A dial to turn the spindle is located outside the bottom of the package for use by the consumer. As the consumer uses the product, the dial is turned to move the elevator towards the top of the package, pushing up the product stick. By turning the dial in the opposite direction the product stick can be retracted.
One method of manufacturing such products is known as the bottom-fill method. The desired shape is generally achieved by providing a package having an oval or circular cross-section and a cap, of the same cross-section, on the top of the package. The cap has a smooth concave inner surface which is adapted to function as a mold in forming the top of the stick. The product, in its molten state, is poured into the package from the bottom. While the product is still in a molten or liquid form, the elevator/screw system is attached to the bottom of the container and the bottom is sealed. The product and container are then allowed to cool, whereby the product takes on the desired shape. An example of this bottom fill method can be found in U.S. Pat. No. 4,369,158 issued to Woodruff et al. on Jan. 18, 1983.
Another method used to manufacture shaped stick-type products is known as the fill/invert method. This method achieves a product with the desired shape by providing a package having an oval or circular cross-section, but with a closed bottom already having the elevator/screw system attached. The product is poured into the package from the top and the top of the package is sealed by a cap having a smooth concave inner surface for molding the end of the stick. The package is then inverted so that some of the molten product flows from the bottom of the package to the top to fill the outage volume intermediate the original fill line and the cap. The package is kept in this position during cooling.
Because the cosmetic products are often composed of a large proportion of volatile materials, such as alcohol, it is necessary to seal the package thoroughly, prior to use by consumers, in order to prevent the escape of these materials during manufacture, shipment and storage. When the package is not effectively sealed, volatiles evaporate and the product shrinks, losing its shape, fragrance and aesthetic appearance. A major problem of sealing these packages has been to provide an effective sealing means on the bottom of the package, where the elevator/screw system is attached. The screw shaft of these packages extends through a hole in the bottom of the where it is attached to a dial. Product in either its molten or volatile state has access to this hole where it can escape.
One way to avoid this problem is to use a push-up dispensing system rather than the elevator/screw design. With such a system there is no hole in the bottom because no elevator shaft or dial means is needed to dispense the product. However, as mentioned earlier, consumers prefer the elevator/screw design to other dispensing systems.
Another way to prevent volatiles from escaping, but using an elevator/screw design, is described in U.S. Pat, No. 4,950,094 issued to Yorks on Aug. 21, 1990. This device uses a resilient washer placed between the dial and the bottom wall of the package. The design is effective in sealing the hole in the bottom of the package where the screw shaft extends through. However, when using the bottom-fill method this hole is not the only place on the bottom of the package that needs to be sealed. In bottom fill packages the bottom wall is not integral with the package but must be attached after filling. The base must be sealed to the side walls to prevent the escape of volatiles therefrom. While the washer of the Yorks patent seals the interface of the screw shaft and the base of the package it does nothing to prevent the escape of volatiles from the junction of the base of the package and its sidewalls.
Therefore, the fill/invert system is preferred over the bottom-fill method, since the base of the package is integral with the sidewalls and does not need to be sealed. When fill/invert packages are filled, molten product is poured from the top of the package where it flows past the elevator through apertures in the elevator platform, and down to the bottom of the package. Leakage of molten product occurs through the hole on the bottom of the package where the screw shaft extends. Furthermore, as with the bottom fill packages, even after the product is solidified, volatile materials evaporate and escape through this hole. The washer of the Yorks patent does an effective job of sealing the hole on the bottom of fill/invert packages.
However, the washer design of the Yorks patent has many drawbacks. The assembly step involved complicates the manufacturing process and requires secondary assembly. Furthermore, the resilient washer is expensive and adds to the cost of the final product.
It is therefore an object of the present invention to provide a cosmetic package that effectively seals against leakage of molten product and volatiles, but which is easy to manufacture and inexpensive.
It is another object of the present invention to provide a cosmetic package with an elevator/screw dispensing system, and which seals against loss of product, whether in a molten or volatile state, by containing all of the product within or above the elevator thereby preventing it from reaching the bottom wall and the hole therein.
It is yet another object of the present invention to provide a process for making a cosmetic stick in the container set forth above using a fill/invert method.